Method for forming a composite plastic structure



Aug. 26, 1952 E. L. DANIELSON ET AL 7,

METHODFOR FORMING A COMPOSITE PLASTIC STRUCTURE Filed Jan. 2, 1951 5 Sheets-Sheet 1 INVENTOI Q. ELMER L-DANIELSON F.L.OYD J- DOF'SEN ATTO RNEYS Filed-Jan.

E. L., DANIELSON ET AL METHOD FOR'FORMING A COMFIOSITE PLASTIC STRUCTURE 5 Sheets-Sheet 2 INVENTOR.

ELMER L DANIELSON F L OYD J- DOFSEL N A TTORN EYS Aug. 26, 1952 E. DANIELSON ET AL 2,607,957

METHOD FOR FORMING A COMPOSITE PLASTIC STRUCTURE Filed Jan. 2, 1951 :IUSZ: :3a. 1322a 5 Shgts-Sheet 4 TTORNEYS Aug. 26, 1952 E L. DANIELSON ET AL METHOD FOR FORMING A COMPOSITE PLASTIC STRUCTURE.

5 Sheets-Sheet 5 Filed Jan. 2, 1951 as? 558; I 38} m 36 ///Av/ a;

I J31; --H

, INVENTOR.

E LMER L DAN\EL $ON LYOYD J- DoFsz WV A 'r TOR N EYS i Patented Aug. 23, 1952 METHOD FOR FORMING A COMPOSITE PLASTIC STRUCTURE Elmer L. Danielson, Oakland, and Floyd J. Dofsen, San Francisco, Calif.

\ Application January 2, 1951, Serial No. 203,992

8 Claims.

The; present invention relates to improvements in a method for forming a composite plastic structure. It consists of the steps of the method as hereinafter described and claimed;

An object of our invention is to provide-a composite plastic structure,'composed of at leasttwo parts, which are mechanically interlocked during the casting operation. Broadly speaking, these structures may be key caps for calculators or typewriters, telephone dials, stove knobs, etc. Such structures are mentionedby wayof illustration only, and we. do not. Wish to belimitedg in'this respect. i

Briefly stated, we cast a first part of the plastic structure, with projections extending from a 'sur-' face thereof against which a second plastic part is to be cast. This precast part is placed in ,a cavity provided in one die ofa mold, and thereafter a second die is moved into coacting relation with the first to close-the mold. During the closing of the mold, the projections are automatically deflected, or unset,- and are retained in these positions by the dies. Upon injecting the material for the-second plastic part of the composite structure, it is conveyed 'over'the surface of the precast part and around the projections to embed the latter therein; Thus the projections mechanically interlock. the two plastic parts. i

Other objects and advantages will appear as the-specification continues. The novel features of the. invention. willbe setiorth-in the'claims hereunto'appendedl 7 Drawings Fora better understanding of our invention,

reference should be had to. the accompanying. drawings,v forming. part of this application, in.

die,, and asecond die. moved into position. relative to thev first. die. to. closeuthevcavity and to deefiect the projections; 1

Figure 4 is ayiew. similar to Figure 3, but ..dis-

closing. the. plastic .imaterial for the second part castagainst. the first,.the.two partsof .the com.- posite stoveknobbeing. interlocked;

Figure. 5.is. at rear elevational view .oi-the come pletedstoveknob; V

Figure 6 is a front elevational view of the-same: knob; :1 Figure 7 is -a side elevational'viewof the com pleted knob, portions being shown'in section;

Figure 8 is a rear elevational view of a precast part for a key cap on which oppositely-tapered projections are provided; Y Figure 9 is a vertical sectional view: taken along the line IX-IX of Figure 8', parts being shown in elevation; t

Figure 10 discloses this precast part (Figure-8) disposed in a mold die cavity, with-a second die inserted into the "first die so as to close the-cave ity, the projections on the precast part being de fiected or upset in opposite'directions; 1 Figure 11 is a View similar to Figure 10,1aitei' the injection of the-plasticmaterial for the sec?- 0nd part of the key cap has been completed; Figure 12 is an elevational view, partly in fsection, of thisfirst form of the key cap; f

Figure 13 is a rear view of a second form of a. precast part for a key cap, wherein projections having conical-shaped indented endsare provided;

Figure l4 is a sectional viewtakenalongthei line XIV-XIV of Figure 13', partsbeingshown" in elevation;

Figure 15 discloses the precast partof this sec-- ond modified key cap (Figure 13) disposed in1 the dies of a closed mold; I v

Figure 16 is aview' similar to Figure- 15, after}- the injection of the plastic material for-the section, taken along the line= XIX-XIX of Figure 18; e

Figure" 20 illustratesthi-s' third formof-theprecast part of a keycap as being disposedei-n the closed dies of a mold;

Figure 21 is a view corresponding 'to but showing the plastic material for the second part of the key cap injected into the closed mold;

and I 1 Figure 22 is anelevational View, partly insection, of the 'thirdembodiment of-our key ca-p.--

While we have shown only the preferreduformsr of our invention, itshould be-understood lthatlf various-changes, or modifications, may he made withinrthe scope of theannexed claimsw-ithout departing from the spirit thereof. I

OFFICE.

Figure "20,

Detailed description sequently-cast second part C that are mechani- V cally interlocked by projections 10.

As illustrated in Figures 1 and 2, the precast part B is fashioned with a downwardly con- H verging frusto-conicaI shell H having an outwardly-extending annular flange l2 at its top.

Within the bore I4 of this shell, we'provide an upwardly-extending frusto-conical flange l 5, the

latter being formed with an opening It at the top thereof. Reinforcing gussets I! are arranged between the shell II and the internal flange IS. The projections I are carried by and rise from the upper surface of the flange l5.

- The first part B is cast from suitable plastic material, with the shell. I I, internal flange l-5, gussets I1 and projections I!) being formed into an integral unit. In Figure 1, We show slots IB piercing the flange 15 to define the word Off (also, see Figure 6).

Turning now to Figures 3 and 4, we disclose a mold indicated generally at D. This mold includes lower and upper dies E and F, respectively. 'In its structural features, the lower die defines a cavity l9 extending downwardly there-' into from the up er surface 2a of this die. The walls of the cavity are shaped to correspond with and support the exterior surfaces of the shell H and its external flange l2. Also, the bottom 2| of this cavity bears against the underneath surfaceof the internal flan e iii. A slightly-concaved recess 22 is provided in the bottom of the cavity immediately below the opening 16;

' After the precast part B has been disposed in the cavitv of the lower die E, as shown in Figure 3, with the pro ections l0 extending upwardly, the up er die F is moved into coacting relation with the lower die to close the mold. As clearly shown in Figures 3 and 4, the upper die has a core 23 extending downwardly into the cavity I 9 when the lower surface 24 of the die F abuts the upper surface 20 of the die E.

The core 23 has a frusto-conical underneath surface 25. which conforms to the ta er of the internal flange 'l of the recast part B. As the mold is closed; the'c'ore 23 will deflect the projec'tions Ill automatically, inclining them toward the vertical axis 26 of the precast part. A

When the dies E'and F are brought to ether, a space 21 above the upper surface of the internal flange [5 receives an "injection of plastic material, which forms the cast second part C. This space communicates with an annular groove 28, which is fashioned in the upper die. An orifice 29 receives the plastic material from an injection nozzle (not shown), and conveys this material to the annular groove 28. Thence the materiaYflows into the space 21, and spreads out over the upper surface of the internal flange of the precast first part B. I

' Moreover, the incoming plastic material flows around and embeds the deflected projections H), and extends through the opening [5 into the concaved recess 22.. Part of this material will find its waythrough the slots l8,producing the word Off. It will benoted that the core 23 holds the projections In in their deflected posiing between the hub 30 and the shell H.

tions during the casting of the second part of the composite plastic structure.

The plastic material entering the annular groove 28 will provide a hub 30 on the final product (see Figures 5 and 7). The upper die F has radially-extending grooves 3 I therein, which receive the gussets l1 and convey a portion of the incoming material to form webs 32 extend- These webs embed the gussets l1 therein (see Figures 5 and 7)".

For the purpose of securing the knob A to the control stem of a gas valve on a stove, the upper die F includes a central core 33. This core produces a stem-receiving bore 34 within the hub 30,'which is non-circular in cross-section (see Figure 5). 7

Upon separating the, dies of the mold, the completed stove knob A may be readily removed therefrom. The deflected. i projections 16 pro-- vide mechanical interlocks between the parts'f'B' and "C of the plastic structure. As previously ointed out, our method is not to be limited to the production of stove knobs. Thetwoparts of the composite plastic structure maybe made in any contrasting colors desired. For the purpose of illustration, the precast part B has been shown in white, while the part C has been 'shaded to indicate red.

Itwill be noted from Figures8 to 12, inclusive,

that we provide.akeycap designated generally at G; This composite plastic structure includes a precast first part H and a subsquentlyrcast second part J.- Inthe final product, as. shown in Figure 12, the part H becomes a face'member for the can. while the part J forms the shell-like body for the key cap.

In Figures 8 and 9, we disclose the precast first part as including a base 35 having an upstanding marginal flange 36 extending around the perimeter thereof. The base is fashioned with a slot 31 throu h which material of the part J extends in the final product to producea desired character. 'As herein illustrated, this character consists of the letter O. s

' The precast part H further'has projections 3 8 formed integral with and rising from the base 35. When this part is made, the upper ends 39' of these proiections are bevelled in the manner shown in Figure 9. 7

For the purpose of completing the key cap (5 after the precast part H hasbeen made, we provide a mold designated generally atK in'Fi ures 10 and 11. This mold includes upper and lower dies L and M, respectively. The lower die has a cavity 40 therein, which is designed to receive and su port the precast first part H (see Figure. 10) with the base 35 resting on the bottom 4| of part J of the final structure is injected throu h an orifice 44 into the unoccupied spacelli of the die cavity. While thel proiections areheld. in

upset positions, the incoming plastic material flows over theupper surface 46 of thejbase 3'5 and embeds the projections; and at the same time, provides the body J for the key cap.

Upon opening the mold K, the completed key inclusi e. a e. very... .Silllllhl'1=.:.0 the embodiment just described; Accordingly, like reference numerals will be applied to corresponding parts; Now the differences will be pointed out, in which the letter a will be added to the reference numerals of the changes.

As shown in Figures 13 and 14, the projections 38a on the precast part H have conical-shaped recesses 39a fashioned in the upper ends thereof. The lower ends of the cores 42a carried by the upper die L are tapered, as at 43a. Accordingly, when the mold K is closed, the projections 38a will be spread outwardly, or upset, in the manner shown in Figure 15. These upset projections provide mechanical interlocks between the parts H and J of the modified key cap G Otherwise, the construction and operation of the mold K and the final product are the same as that previously described in connection with Figures 8 to 12, inclusive.

Likewise, the third modification of the key cap G and the modified mold K disclosed in Figures 18 to 22, inclusive, are similar to the forms disclosed in Figures 8-12 and 13-17. The same reference numerals have been used to designate corresponding parts. The letter 1) has been added to the changed portions.

It will be noted from Figures 18 and 19 that projections 3812 are fashioned on the precast part H so as to have V-shaped grooves 39b in their upper ends. The cores 421) on the upper die L of the mold K have wedged-shaped lower ends 4%. The part H is placed in the cavity 49 of the lower die M, with the projections 38b extending upwardly. Upon closing the mold, as shown in Figure 20, each projection is upset or spread in opposite directions.

Upon injecting the material into the mold to form the subsequently-cast part J, the upset projections 38b will be embedded therein, with these projections providing mechanical interlocks between the two parts of the plastic structure.

In all forms disclosed herein, projections are provided on the precast first part near the outer edges thereof. This will prevent shrinkage of the subsequently-cast part. Also, portions of the upper die hold the projections in deflected or upset position during casting of the second part.

We claim:

1. In the herein described method of forming a composite plastic structure, which includes the steps of: precasting a plastic first part of the structure with spaced-apart projections extending from a surface thereof against which a second part is to be cast subsequently; deflecting these projections into angular positions relative to said surface, while maintaining the first part and the projections in a solidified condition; and thereafter injecting heated plastic material for a second part of the structure against said surface for flowing around and embedding the deflected projections, while still holding the projections in their deflected positions until the second part solidifies, whereby the angularlydisposed projections will be precluded from returning to their original positions and will mechanically interlock the two solidified parts.

seam

:2. Thecombination.jasvset:forth-Jniclainri in: which the proiectionsjrare deflected toward he:

another so as to resist separation of the two parts. 32' In the. described m od of min a c0mpo sit .p1ast ig structure, which includes the steps of: precasting a plastic first part of the structure with at least one projection extending ir a urfac here f a a st hi h. a ec part is to be cast subsequently defiecting j this projection into angular position relativeto said surface, while maintaining the first part and the projection in a solidified condition; and thereafter injecting heated plastic material for a second part of the structure against said surface for flowing around and embedding the deflected projection, while still holding the projection in its deflected position until the second part solidifies, whereby the angularly-disposed projection will be precluded from returning to its original position and will mechanically interlock the two solidified parts.

4. In the herein described method of forming 'a composite plastic structure, which includes the steps of: precasting a plastic first part of the structure with at least one projection extending from a surface thereof against which a second part is to be cast subsequently; upsetting the end of this projection to provide an enlarged head overlying and spaced from said surface, while maintaining the first part and the projection in a solidified condition; and thereafter injecting heated plastic material for a second part of the structure against said surface for flowing around and embedding the projection and its head, while still holding the end of the projection in its upset condition until the second part solidifies, whereby said end of the projection will be precluded from returning to its original position and will mechanically interlock the two solidified parts.

5. The combination of steps as set forth in claim 4, in which the projection is formed initially with a bevelled end, and the latter is deformed laterally during the upsetting thereof.

6. The combination of steps as set forth in claim 4, in which the projection is formed initially with a conical-shaped recess end, and the material near this end is expanded outwardly in radial directions during the upsetting thereof.

'7. The combination of steps as set forth in claim 4, in which the projection is formed initially with a substantially V-shaped groove in its end, and the material near this end is expanded outwardly in opposite directions during the upsetting thereof.

8. In the herein described method of forming a composite plastic structure, the steps of: precasting a plastic first part with at least one projection extending from a surface thereof against which a second part is to be cast subsequently; placing this precast part in a cavity of a first die, with the wall of this cavity supporting the precast part, and the projection extending toward an open end of the cavity; moving a second die into coacting relation with the first die to close the open end of the cavity, while utilizing the second die to deflect and hold the projection in angular position relative to said surface; and thereafter injecting heated plastic material into the unoccupied portion of the die cavity to cast a second part of the structure against said surface, which embeds the deflected projection therein, while the second die still holds the projection in its deflected position until the second part solidifies, whereby the angularlydisposed projection will be precluded from re- 7 tu'rning'to its original position and. will mechanically interlock the two solidified parts.

ELMER L; DANIELSON. FLOYD J. DOFSEN.

file of this patent:

Number I .UNITED sTAT-E's- 'rwrrizuq'rs Name 7 Date Searles Oct. 10,1916 Apple Nov. 12,1918 Schumacher Dec 27, 1921 Hilfreich f May 8, 1928 Hansen Dec. 1, 1936 Watson Nov; 26, 1940 

